Candidates have until Aug. 22 to file paperwork to run; other candidates could enter the race in the coming months.

In Louisiana, all candidates who qualify for the ballot run on Election Day in November. If no candidate receives at least 50 percent of the vote, the top two vote recipients continue to a runoff in December.

The large number of Republicans will split the GOP vote in this district, so Edwards is likely to make it to the runoff, according to Louisiana political operatives.

But Edwards faces an uphill climb in a runoff versus a Republican. GOP presidential nominee Mitt Romney won the 6th District with 66 percent in 2012.

Cassidy is leaving the House to challenge Sen. Mary L. Landrieu, D-La., in one of the cycle’s most competitive Senate races.

Louisiana’s 6th District is rated a Safe Republican contest by Rothenberg Political Report/Roll Call.